Effects of vegetation on turbulent flow structure in groyne fields

ABSTRACTFlow recirculation in groyne fields promotes accumulation of fine sediments and development of riparian and aquatic vegetation. Although flow hydrodynamics in groyne fields is subject of intensive ongoing research, knowledge of vegetation effects on recirculating flow remains lacking. This paper reports the results of field experiments in a natural river comprising large-scale groyne models populated with rigid and flexible artificial vegetation. In the experimental runs population density, submergence ratios, and vegetation types were varied. The results show that vegetation rearranges twin-circulation flow into slow backwater flow. The magnitude of backwater flow is controlled by the bio-mechanical properties of vegetation. The hydrodynamics of the flow interface between the main river and groyne fields was only slightly altered by vegetation. Analytical models of flow at the interface and inside vegetated areas agree well with these experimental results.